Security researcher Nitesh Dhanjani, who alerted Apple of the flaw in May 2008, says the threat of an attacker exploiting this bug is alive and well today, especially with the growth in popularity of Safari and OS X. He says in 2008 Apple told him it didn't consider the issue a security vulnerability but more of a design issue, and that it didn't have plans to fix it anytime soon.
Dhanjani says the vulnerability could let a bad guy download malicious binaries and data files into the browser's Downloads folder without the user knowing because Safari does not ask the user whether he wants to save the file on his machine, which most other browsers do. So when a user visits a malicious website, Safari would allow the site to download files without prompting the user. "It just drops them into the Downloads folder and can serve you thousands of files without your knowing," Dhanjani says.
The main threat the flaw poses is a denial-of-service attack on the victim's machine, he says. The carpet bomb DoS attack would wipe out a session and "whatever you were working on would be gone," he says.
Google's Chrome browser has a similar issue, notes Robert "RSnake" Hansen, CTO at SecTheory. "It automatically downloads files without user prompting, as well, as long as they aren't .exe or whatever," Hansen says.
And the no-prompt download features in Safari and Chrome can be exploited in even more nefarious ways, Hansen says, such as with tools including 42.zip. "You can do some really nasty stuff when you get something like 42.zip involved," he says. 42.zip basically contains multiple zipped files within zipped files that eventually max out file space once they are extracted.
Dhanjani says the only indication of the malicious files downloading would be the pop-up window showing a download, but by then it's probably too late for the victim to do anything about it. Apple does have a security feature in OS X that asks the user if he wants to open an executable that was dropped onto his machine, however, Dhanjani says.
Targeted attacks, such as those against Google and other companies in Operation Aurora, started by dropping a malicious file onto a desktop, he notes. "If I'm an attacker and I spray 100 corporate users [with this executable], someone is going to click on it," Dhanjani says.
It also banks on the user eventually opening up a malicious file that had been downloaded. "It hopes that in two months you'll open it, wondering, 'What is this?'" he adds.
While DoS is a relatively low-tech issue, Dhanjani says, the flaw could be used to wage a blended attack, with, say, a buffer overflow exploit. "It could [also] open up most of your apps without your knowing it," he says, and litter them with malicious data that could be used to further compromise the machine -- and the network.
SecTheory's Hansen says one scenario with a carpet bomb attack would be if Chrome were forced to download a Flash file onto a Vista machine also running Internet Explorer. "Later on, you [the victim] use Internet Explorer and they [the attacker] iFrame in that content," he says. "It would fire an exploit, but ... [the attacker] would have to know the user name ahead of time. So you'd have to do one of those cut-and-paste exploits or SMB decloak to get the user name ahead of time.
"That shouldn't be too hard as long as you know that [the victim] switched between Chrome and IE often on the same site that the attacker controls," Hansen says.
Meanwhile, Dhanjani posted a demo and some examples of a carpet bomb attack.
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